Water absorbent polymers and a process for their preparation

Abstract

Water absorbent polymers and a process for their preparation are disclosed. The process for preparing water absorbent polymers comprises preparing a slurry with relatively high amounts of polymer particles (in the range of 40 to 55 wt % of the total mass of the slurry) having water absorbed therein. The slurry is then directly spray dried to obtain water absorbent polymers.

The invention claimed is: 
     
       1. A process for preparing a water absorbent polymer, said process comprising the following steps:
 i. preparing by inverse suspension polymerization, a slurry comprising polymer particles having water absorbed therein, wherein said polymer particles are present in an amount ranging between 40% and 55% of the total mass of the slurry; 
 ii. homogenising the slurry with the help of heat and stirring, to obtain a homogeneous slurry; and 
 iii. spray drying the homogeneous slurry in a spray drier to obtain water absorbent polymer particles. 
 
     
     
       2. The process as claimed in  claim 1 , wherein the method step of preparing the slurry comprises the following steps:
 (a) partially neutralizing an aqueous monomer solution of a pre-determined concentration by an alkali solution of a pre-determined concentration, to obtain a partially neutralized aqueous monomer solution; 
 (b) adding a pre-determined weight proportion of at least one cross-linking agent and at least one free radical initiator to the partially neutralized aqueous monomer solution, to obtain a resultant solution; 
 (c) mixing at least one organic solvent with at least one dispersing agent under continuous stirring, at a pre-determined temperature, to obtain a non-aqueous mixture; and 
 (d) dispersing said resultant solution drop by drop into the non-aqueous mixture under continuous stirring at a temperature ranging from 55 to 110° C. for a time period varying from 60 to 180 minutes to obtain the slurry. 
 
     
     
       3. The process as claimed in  claim 2 , wherein the monomer includes at least one monomer selected from the group consisting of acrylic acid, methacrylic acid, sodium acrylate, potassium acrylate and acrylamide. 
     
     
       4. The process as claimed in  claim 2 , wherein the cross-linking agent includes at least one compound selected from the group consisting of N,N′-methylenebisacrylamide, ethylene glycol diacrylate, polyethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, glycerol triacrylate, glycerol trimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, and triglycol diacrylate. 
     
     
       5. The process as claimed in  claim 2 , wherein the free radical initiator is at least one compound selected from the group consisting of potassium persulfate, sodium persulfate, ammonium persulfate, alkali metal salts, sulfites, thiosulfates, ascorbates, ferrites and combinations thereof. 
     
     
       6. The process as claimed in  claim 2 , wherein the organic solvent includes at least one solvent selected from the group consisting of cyclohexane, N-hexane, N-heptane and toluene. 
     
     
       7. The process as claimed in  claim 1 , wherein the step of homogenizing the slurry in method step (ii) is carried out at a temperature ranging between 40° C. and 50° C. 
     
     
       8. The process as claimed in  claim 1 , wherein the inlet and outlet temperature of the spray drier is in the range of 70 to 220° C. and 70 to 140° C., respectively. 
     
     
       9. The process as claimed in  claim 1 , wherein the spray drying of the homogeneous slurry is carried out at a feed rate varying between 0.5 to 1.5 kg/hr aspirator speed varying between 1300 and 2800 rpm, and under vacuum varying between m −70 and −170 mm of water. 
     
     
       10. The process as claimed in  claim 1 , wherein the spray drying of the homogeneous slurry is carried out using nitrogen as a drying medium. 
     
     
       11. The process as claimed in  claim 1 , wherein the water absorbent polymer obtained is a copolymer.